Question

UV light effect the DNA by causing

• A. G-G dimerization
• B. G-C dimerization
• C. T-T dimerization
• D. A-T dimerization

Hint:

• UV radiation is a common environmental mutagen.
• It primarily causes the formation of covalent bonds between adjacent pyrimidine bases (C or T) on the same DNA strand, forming pyrimidine dimers.
• Thymine dimers (T-T) are the most prevalent type of UV-induced DNA damage.
• These dimers can interfere with DNA replication and transcription. Cells have repair mechanisms (e.g., photoreactivation, nucleotide excision repair) to fix them.

Answer 1

The Correct Option is C

Ultraviolet (UV) radiation, particularly UV-B, is a known mutagen that can cause specific types of DNA damage. The most common type of UV-induced DNA damage is the formation of pyrimidine dimers. These dimers form between adjacent pyrimidine bases (Thymine - T, or Cytosine - C) on the same DNA strand. The most frequent pyrimidine dimers are:

• Thymine dimers (T-T dimers or T<>T): Two adjacent thymine bases become covalently linked. This is the most common type.
• Cytosine dimers (C-C dimers) can also form.
• Thymine-cytosine dimers (T-C or C-T dimers) can also form.

These dimers distort the DNA helix and can block DNA replication and transcription if not repaired. Purine-purine (e.g., G-G, A-A) or purine-pyrimidine (e.g., A-T, G-C) dimerization is not a typical lesion caused by UV light in this manner. Therefore, UV light primarily causes pyrimidine dimerization, with T-T dimerization being very common. Option (c) "T-T dimerization" is the correct answer. \[ \boxed{\text{T-T dimerization}} \]